Roles of dietary glycine, proline, and hydroxyproline in collagen synthesis and animal growth.
Level 5 - mechanism / opinion, no new human data
Narrative review of animal biochemistry and nutritional mechanisms.
PubMed 28929384 · doi:10.1007/s00726-017-2490-6
What was done
This narrative review synthesized biochemical and nutritional evidence on the endogenous synthesis of glycine, proline, and hydroxyproline (Hyp) in mammals, birds, and fish. It examined their roles in collagen synthesis, growth, and feed efficiency, as well as the practicality of dietary sources such as hydrolyzed feather meal (HFM).
What was found
Glycine, proline, and Hyp account for 57% of the total amino acids in animal collagen. While livestock synthesize proline from glutamine and glutamate in the small intestine, this pathway is absent in birds and possibly most fish. Endogenous synthesis of these three amino acids was reported to be inadequate for maximal growth, collagen production, and feed efficiency in pigs, chickens, and fish. Hydrolyzed feather meal contains 9% glycine, 5% Hyp, and 12% proline, representing a potential low-cost dietary source. No specific trial effect sizes or statistical values were reported in the abstract.
Why it matters
It highlights that glycine, proline, and hydroxyproline function as conditionally essential amino acids required in dietary rations to optimize connective tissue development and growth in livestock and aquaculture.
Limits
The review lacks systematic methodology, quantitative pooled analyses, and individual study sample sizes. Data focus exclusively on animal nutrition and production metrics, limiting direct application to human health or clinical practice.
Cited by
- supports Hydrolyzed collagen powder contains a significantly higher concentration of proline, glycine, and hydroxyproline than steak.